The present invention relates to a method of manufacturing a semiconductor device and, more particularly, to a method of manufacturing a semiconductor device having an impurity region of one conductivity type and an impurity region of the other conductivity type which are self-aligned on a semiconductor substrate.
A method of forming p- and n-type impurity regions using a conventional self-alignment technique will be exemplified as formation of a buried region and an epitaxial layer formed in a subsequent step with reference to FIGS. 3A to 3D.
As shown in FIG. 3A, a thin oxide film 2B is formed on a semiconductor substrate 1 by thermal oxidation. An anti-oxidation film such as a nitride film 7A is formed on the oxide film 2B by an epitaxial growth method or the like.
As shown in FIG. 3B, a photoresist (not shown) is applied to the nitride film 7A and is patterned using a photoetching method. The nitride film 7A or the oxide film 2B is etched using the resultant resist pattern as a mask. After the resist pattern is removed, arsenic ions having a high concentration are selectively implanted in the resultant structure using the nitride film 7A as a mask, thereby forming an n-type impurity region 3.
As shown in FIG. 3C, in order to form a self-aligned p-type impurity region, the resultant structure is selectively oxidized using the nitride film 7A as a mask to form a thick oxide film 2C on the n-type impurity region 3. The nitride film 7A or the oxide film 2B is removed, and boron or the like is doped using the thick oxide film 2C as a mask to form a p-type impurity region 5.
Finally, as shown in FIG. 3D, the oxide films 2C and 2D on the semiconductor substrate 1 are entirely removed by etching or the like, and then an epitaxial film 6 is formed on the entire surface of the semiconductor substrate 1.
In the step of forming an impurity region in the conventional method of manufacturing the semiconductor device, as described above, when the p-type impurity region 5 is to be selectively formed, selective oxidation is performed using the patterned nitride film 7A as a mask. The thick oxide film 2C is formed, and the nitride film 7A is removed. Finally, the p-type impurity region 5 is formed using the thick oxide film 2C as a mask. For this reason, when the thick oxide film is removed from the semiconductor substrate 1, a step is formed in a boundary between the p- and n-type impurity regions 5 and 3, as shown in FIG. 3D. In addition, even if epitaxial growth is performed on the entire surface of the substrate, the step is left on the surface of the epitaxial film 6. In a subsequent step, when the surface layer of the epitaxial film 6 for isolating an element region is selectively thermally oxidized to form an element isolation oxide film 8, stress is concentrated on the step of the epitaxial film 6 at the boundary between the p- and n-type impurity regions to cause crystal defects. As a result, an error occurs in the resultant semiconductor device.